This invention relates generally to flow control valves. More specifically this invention pertains to valves including rotary valves and butterfly valves used in locomotive cooling systems. In addition, the present invention pertains to methods for refurbishing such valves.
Rotors are known for use in applications where a source of fluid must be selectively directed to one of several destinations. Such valves have a rotor that can be rotated about its longitudinal axis in a chamber of a valve body. A valve stem on top of the rotor is connected to an actuator that controls the rotation of the rotor in the valve body. A top cover plate mounted to the top of the valve body has an opening through which the valve stem protrudes. An o-ring is attached to the valve stem base to seal the valve chamber and prevent fluid from leaking from the valve body.
Some larger industrial valves, or rotors used in large vehicles such as locomotives may endure up to about one million cycles. Over time, however, the valve chamber and rotor are exposed to very hot corrosive fluids; the o-ring deteriorates and separates from the valve stem base, or corrosion forms on the surface of the valve stem base. In addition, grooves may form on the valve stem because the hardness of the surface is compromised and exposed to the top cover plate because the o-ring has deteriorated.
All these factors alone, or in combination, lead to the fluid leaking from the valve chamber. Leaking from closed systems, such as a cooling system in a locomotive is unacceptable. Such systems require zero leaking. For example one drop per minute from such systems is considered significant and will adversely affect the performance of the system and locomotive. Moreover, fluid may leak from the valves onto other components of the locomotive potentially damaging such components.
Similar failure modes can be found in butterfly valves, which are mounted in a flow line and operate between an open and closed position to allow the free flow of fluid and stop the flow or fluid respectively. A typical butterfly valve includes a housing including two semicircular portions affixed to one another. A disc, the valve portion, is mounted within the housing on two diametrically opposed valve stems that are inserted through similarly opposed apertures. An actuator, connected to one of the valve stems, controls movement of the disc by rotating the valve stem about its longitudinal axis.
Typically, the valve stem is connected to a shaft, which is connected to the actuator. The valve stem and shaft are encased within a casting. A bushing, or similar fitting, supports the shaft within the housing. An o-ring is disposed between the outside surface of the bushing and inside surface of the casting to form a seal between the bushing and casting.
A seal is affixed to the inside surface of the housing to prevent leaking from the housing. However, fluid tends to leak at the junction of the seal and valve stem. Over time, the o-ring between the bushing and the casting will deteriorate and separate from the bushing and casting, causing fluid to leak into the actuator, which may eventually fail.